This invention relates to hydraulic cylinder seals and more particularly to a novel seal structure especially adapted for use in large diameter high pressure hydraulic cylinders.
Hydraulic presses are well known for use in forging, extrusion, deep drawing and the like. Such hydraulic presses employ a ram member supported in a cylinder and driven by a fluid under pressure to exert force on the material being formed. Oil is commonly used as the pressure fluid for operating the ram and the oil may be at a pressure of 10,000 pounds per square inch. Hydraulic presses of this general type are shown in U.S. Pat. No. 2,997,353 to A. Zeitlin et al and U.S. Pat. No. 3,156,475 to Gerard et al.
Very large hydraulic cylinders which must contain extremely high fluid pressures may expand or "breathe" up to 0.002 or more inches for each inch of diameter of the cylinder. For a forging press having a capacity of 200,000 tons, the ram cylinder may have a diameter of 100 inches. A 100-inch diameter cylinder can increase its diameter as much as 0.2 inch with an internal pressure of about 10,000 p.s.i. This would then increase the gap between the interior diameter of the cylinder and the outer diameter of the ram received by the cylinder by 0.1 inch or more, depending on the ram design. The dynamic seal which is used between the ram and the cylinder wall for containing the high pressure fluid cannot easily bridge the gap when it is increased by 0.1 inch and the seal can extrude into the gap, thereby decompressing the cylinder and making the machine inoperable.
Dynamic seals which have been used are of many different types and, for example, can be of rubber, steel or fabric having impregnated asbestos therein. The seals can have the shape of a V-ring or O-ring, or the like.
Above noted U.S. Pat. No. 3,156,475 to Gerard et al describes the problem of expansion of the cylinder in very high pressure hydraulic presses and the loss of the seal to the ram under this condition. Gerard et al propose a seal fastened to the end of the ram and by a support ring. The ring is caused to expand and contract with the cylinder to maintain a seal to the cylinder, even though the cylinder breathes. The design of structures of this type is complicated by requiring a secondary seal between the seal-carrying ring and the ram and by requiring a ring design which will expand in a manner to track the expansion and contraction of the cylinder wall.
The problem of the expansion of the cylinder wall of a high pressure hydraulic ram-type structure is also referred to in U.S. Pat. No. 4,173,881 to Rose. In that patent, a liner which extends the full length of the cylinder wall. Pressure is applied along the full length of the liner between two input sources which are isolated from one another by a sealing ring between the liner and the cylinder body. This structure relies on its operation for the seal between the auxiliary cylinder liner and the main cylinder body and would fail with the failure of this additional seal.